A phase 1 and randomized controlled phase 2 trial of the safety and efficacy of the combination of gemcitabine and docetaxel with ontuxizumab (MORAb-004) in metastatic soft-tissue sarcomas.

BACKGROUND: Ontuxizumab, a humanized monoclonal antibody, targets endosialin (tumor endothelial marker 1 [TEM-1] or CD248), which is expressed on sarcoma cells and is believed to be involved in tumor angiogenesis. This is the first trial to evaluate ontuxizumab in patients with sarcoma. METHODS: Part 1 was an open-label, dose-finding, safety lead-in: 4, 6, or 8 mg/kg with gemcitabine and docetaxel (G/D; 900 mg/m2 gemcitabine on days 1 and 8 and 75 mg/m2 docetaxel on day 8). In part 2, patients were randomized in a double-blind fashion in 2:1 ratio to ontuxizumab (8 mg/kg) or a placebo with G/D. Randomization was stratified by 4 histological cohorts. RESULTS: In part 2 with 209 patients, no significant difference in progression-free survival between ontuxizumab plus G/D (4.3 months; 95% confidence interval [CI], 2.7-6.3 months) and the placebo plus G/D (5.6 months; 95% CI, 2.6-8.3 months) was observed (P = .67; hazard ratio [HR], 1.07; 95% CI, 0.77-1.49). Similarly, there was no significant difference in median overall survival between the 2 groups: 18.3 months for the ontuxizumab plus G/D group (95% CI, 16.2-21.1 months) and 21.1 months for the placebo plus G/D group (95% CI, 14.2 months to not reached; P = .32; HR, 1.23; 95% CI, 0.82-1.82). No significant differences between the treatment groups occurred for any efficacy parameter by sarcoma cohort. The combination of ontuxizumab plus G/D was generally well tolerated. CONCLUSIONS: Ontuxizumab plus G/D showed no enhanced activity over chemotherapy alone in soft-tissue sarcomas, whereas the safety profile of the combination was consistent with G/D alone.

A phase 2 study of ontuxizumab, a monoclonal antibody targeting endosialin, in metastatic melanoma.

Objectives Ontuxizumab (MORAB-004) is a first-in-class monoclonal antibody that interferes with endosialin function, which is important in tumor stromal cell function, angiogenesis, and tumor growth. This Phase 2 study evaluated the 24-week progression-free survival (PFS) value, pharmacokinetics, and tolerability of 2 doses of ontuxizumab in patients with metastatic melanoma. Patients and methods Patients with metastatic melanoma and disease progression after receiving at least 1 prior systemic treatment were randomized to receive ontuxizumab (2 or 4 mg/kg) weekly, without dose change, until disease progression. Results Seventy-six patients received at least 1 dose of ontuxizumab (40 received 2 mg/kg, 36 received 4 mg/kg). The primary endpoint, 24-week PFS value, was 11.4% (95% Confidence Interval [CI]: 5.3%-19.9%) for all patients (13.5% for 2 mg/kg and 8.9% for 4 mg/kg). The median PFS for all patients was 8.3 weeks (95% CI: 8.1-12.3 weeks). One patient receiving 4 mg/kg had a partial response, as measured by Response Evaluation Criteria in Solid Tumors v1.1. Twenty-seven of 66 response evaluable patients (40.9%) had stable disease. The median overall survival was 31.0 weeks (95% CI: 28.3-44.0 weeks). The most common adverse events overall were headache (55.3%), fatigue (48.7%), chills (42.1%), and nausea (36.8%), mostly grade 1 or 2. Conclusions Ontuxizumab at both doses was well tolerated. The 24-week PFS value was 11.4% among all ontuxizumab-treated patients. The overall response rate was 3.1% at the 4 mg/kg dose, with clinical benefit achieved in 42.4% of response evaluable patients. Efficacy of single-agent ontuxizumab at these doses in melanoma was low.

Targeting endosialin/CD248 through antibody-mediated internalization results in impaired pericyte maturation and dysfunctional tumor microvasculature.

Over-expression of endosialin/CD248 (herein referred to as CD248) has been associated with increased tumor microvasculature in various tissue origins which makes it an attractive anti-angiogenic target. In an effort to target CD248, we have generated a human CD248 knock-in mouse line and MORAb-004, the humanized version of the mouse anti-human CD248 antibody Fb5. Here, we report that MORAb-004 treatment significantly impacted syngeneic tumor growth and tumor metastasis in the human CD248 knock-in mice. In comparison with untreated tumors, MORAb-004 treated tumors displayed overall shortened and distorted blood vessels. Immunofluorescent staining of tumor sections revealed drastically more small and dysfunctional vessels in the treated tumors. The CD248 levels on cell surfaces of neovasculature pericytes were significantly reduced due to its internalization. This reduction of CD248 was also accompanied by reduced α-SMA expression, depolarization of pericytes and endothelium, and ultimately dysfunctional microvessels. These results suggest that MORAb-004 reduced CD248 on pericytes, impaired tumor microvasculature maturation and ultimately suppressed tumor development.

Development of 124I immuno-PET targeting tumor vascular TEM1/endosialin.

UNLABELLED: Tumor endothelial marker 1 (TEM1/endosialin) is a tumor vascular marker highly overexpressed in multiple human cancers with minimal expression in normal adult tissue. In this study, we report the preparation and evaluation of (124)I-MORAb-004, a humanized monoclonal antibody targeting an extracellular epitope of human TEM1 (hTEM1), for its ability to specifically and sensitively detect vascular cells expressing hTEM1 in vivo. METHODS: MORAb-004 was directly iodinated with (125)I and (124)I, and in vitro binding and internalization parameters were characterized. The in vivo behavior of radioiodinated MORAb-004 was characterized in mice bearing subcutaneous ID8 tumors enriched with mouse endothelial cells expressing hTEM1 and by biodistribution and small-animal immuno-PET studies. RESULTS: MORAb-004 was radiolabeled with high efficiency and isolated in high purity. In vitro studies demonstrated specific and sensitive binding of MORAb-004 to MS1 mouse endothelial cells expressing hTEM1, with no binding to control MS1 cells. (125)I-MORAb-004 and (124)I-MORAb-004 both had an immunoreactivity of approximately 90%. In vivo biodistribution experiments revealed rapid, highly specific and sensitive uptake of MORAb-004 in MS1-TEM1 tumors at 4 h (153.2 ± 22.2 percentage injected dose per gram [%ID/g]), 24 h (127.1 ± 42.9 %ID/g), 48 h (130.3 ± 32.4 %ID/g), 72 h (160.9 ± 32.1 %ID/g), and 6 d (10.7 ± 1.8 %ID/g). Excellent image contrast was observed with (124)I-immuno-PET. MORAb-004 uptake was statistically higher in TEM1-positive tumors than in control tumors. Binding specificity was confirmed by blocking studies using excess nonlabeled MORAb-004. CONCLUSION: In our preclinical model, with hTEM1 exclusively expressed on engineered murine endothelial cells that integrate into the tumor vasculature, (124)I-MORAb-004 displays high tumor-to-background tissue contrast for detection of hTEM1 in easily accessible tumor vascular compartments. These studies strongly suggest the clinical utility of (124)I-MORAb-004 immuno-PET in assessing TEM1 tumor-status.